Selecting Optimum Cement Contents for Stabilizing Aggregate Base Materials (7-4920-2)

Researchers designed a laboratory test sequence to identify the optimum amount of portland type I cement for stabilizing two aggregates, limestone and recycled concrete, typically used in the Houston District. Smectitic compositions identified through mineralogical investigations corresponded with the poor performance of the untreated aggregates in preliminary testing and substantiated the need for stabilization. Samples were subsequently treated with 1.5,3.0, and 4.5 percent cement and tested for strength, shrinkage, durability, and moisture susceptibility in the laboratory. Strength was determined with the Soil Cement Compressive Strength Test (TxDOT Test Method Tex-120-E), and a linear shrinkage test was developed to assess shrinkage characteristics. Durability was evaluated with the South African Wheel Tracker Erosion Test (SA WTET), and moisture susceptibility was assessed with the Tube Suction Test (TST). The limestone aggregate was also subjected to modulus testing. Based on these parameters, stabilized samples exhibited markedly improved performance with minimum additions of cement. Based on the results of the laboratory testing, the recommendation of this report is 3.0 percent cement for the limestone and 1.5 percent cement for the recycled concrete. For future testing of aggregate base materials to determine optimum cement contents, the joint utilization of the strength test and the TST is recommended. Sufficient quantities of cement should be added to tested samples to obtain minimum unconfined compressive strengths of 300 psi in the former and maximum average surface dielectric values of 10 in the latter. The minimum amount of cement necessary to satisfy both criteria should be recommended for pavement construction. In addition to these tentative specifications, a provisional pre-cracking procedure is also suggested in this report for further evaluation.